Some TMNT stuff really isn't for little kids.
Oroku Saki was a high-ranking member of the Foot Clan in feudal Japan, and the reincarnation of Takeshi Tatsuo. He orders that in addition to assassinating the lord they were hired to kill, they should wipe out anybody else they come across. Hamato Yoshi, another Foot Clan member, refuses, and Saki marks him for death. The Foot kills Yoshi's wife, Tang Shen, but Yoshi flees with his and Shen's four sons. Some years later, Saki and the Foot find Yoshi and his children, and slay them all. A mystical woman named Kitsune would grant a spell to make Oroku Saki an immortal.
He was laid to rest with the aide of ooze stolen from Krang and Kitsune's mysticism and was resurrected in modern times by Oroku Karai. He encourages her to call him "grandfather" even though they are many generations and several hundred years apart. During his time in stasis, his spirit conquered the realm of the Afterlife, where he learned he was destined to rule the earth world and eventually return to the Afterlife as a lost soul. Knowing the future, he vows to change it by conquering the realm of the Afterlife upon his return.
He is currently at war with Krang for dominating the world and is gathering as much forces as he can. Both the Shredder and Krang are after the mutant technology. He have a female arctic fox mutant in his army and after knowing of other mutants such as the turtles and their master he had Splinter kidnapped and offered him a place at his army. However, Splinter being a reincarnated Hamato Yoshi refused. So Saki ordered his followers to destroy him and when they he face him himself and was about to finish him. However, Splinter was saved by the turtles and Saki knows that they are the reincarnated children of Hamato Yoshi. The turtles make their get away but not before the promised that they will be destroyed.
Later, he was seen displaying his disappointment in Karai's development and tells her that he will find another second in-command. Impressed by Leonardo, he orders his capture and conducts a plan involving kidnapping and stabbing Casey Jones. Shredder then has Kitsune brainwash Leonardo to become his new Chunin and uses him for a show of strength to the criminal underworld. In the Turtles second attempt to rescue Leonardo, his brainwashing dissipates and Karai reveals her secret weapons; Bebop and Rocksteady. Shredder, impressed by her actions and loyalty, reinstates her place as Chunin--seemingly undisturbed by his loss of control over Leonardo.
Shredder calls a meeting with Krang and proposes an alliance in exchange for Utrom technologies, which Krang rejects. A short battle results in retreat on both sides and the revelation that Shredder had stolen some Utrom resources from Krang's compound to begin creating a mutant army.
Oroku Saki fights with Hamato Yoshi in issue 50 and is defeated. Saki commits seppuku with his claws whilst Yoshi acts as his second, cutting his neck from behind. Yoshi subsequently takes over the Foot Clan.
After his death Shredder's body is kept in a crypt that is guarded by Jennika who was assigned by Hamato Yoshi in order to learn humility. Shredder's tomb is eventually desecrated by the witch Kitsune who plans to revive Oroku Saki in order to restore order to the Foot Clan.